Electronic switch



nMarch l2, 1946. J. E. SMITH ErAL 2,396,395

ELECTRONIC SWITCH Filed Sept. 18, 1942 A .MHH-o INVENToRs `:ERNEST SMITH, EUGENE R. sHENK Patented Mar. 12, 1946 ELECTRONIC SWITCH J. Ernest Smith, Jackson Heights, and Eugene R.

Shenk, Brooklyn,

ware

N. Y., assignors to Radio C poration of America, a

orcorporation oi' Dela- Applicltion September 18, 1942, Serial No. 458,808

(Cl. Z50-27) 11 Claims.

This invention relates to an electronic switch. In a variety of applications it is found to be advantageous to perform switching operations by means oi controlled electron discharge tubes. The invention as herein described performs such a switching operation equivalent to that of a double-pole double-throw switch.

It is an object of our invention to provide an electronic switch capable of performing a dual switching function in response to the application of an on-and-oif current in a control circuit.

It is another object of our invention to provide switching means for interchanging the connections between two input circuits and two output circuits.

It is still another object of our invention to provide a reversing switch operable upon the respective inputs of two signaling channels so as to feed these inputs after amplification reversibly to two independent output channels.

Our invention may best be described by reference to the accompanying drawing, the sole figure of which represents diagrammatically a preferred embodiment.

In the drawing we show conventionally two input circuits A and B; also two output circuits C and D. A control circuit E is indicated as having one grounded terminal and one terminal the potentials of which are used by capacitive coupling across a condenser to the control grid of a discharge tube 2.

We show also two ampliiier tubes 3 and 4 which are preferably of the twin triode type. A direct former to control grids I and 8, these control grids being included in the tubes 3 and 4 respectively. I'he input circuit B is coupled across transformer 9 to control grids I Il and II which are individual to the tubes 3 and 4 respectively.

The common cathode I2 in tube 3 is connected to a junction between two resistors RI and R2. The common cathode I4 in tube 4 is connected to the cathode l5 in tube 2 and both these cathodes are connected through a resistor R3 to ground and to the negative terminal of source 5.

Across the terminals of source 5 is connected a voltage divider consisting of resistors R4, R2, and RI. The junction between resistors R4 and R2 is tapped for feeding potential to the anode in tube 2. The control grid I8 in tube 2 is provided with a grid leak resistor R5 connected to ground.

The tube 3 s two anodes I1 and I9.

'I'he anodes Il and I8 are connected in parallel and are fed with anode potential through the primary winding of a transformer 2l. The secondary of this transformer feeds output signal potentials to the channel C.

Anodes I9 and 20 are connected in parallel and both are fed with anode potential through the primary winding of transformer 22. The secondary of this transformer is connected to the output channel D.

The control tube 2 is rendered alternately conductive and non-conductive by virtue oi a square type voltage control signal impressed on the terminals E. By means of this control ltube 2, the tubes 3 and 4 are rendered alternately conductive. When tube 3 conducts, then tube I is blocked and vice-versa.

In order to perform the switching functions satisfactorily, vit is found that certain circuit parameters should be obtained, particularly in reference to the impedance values of the resistors RI, R2, R3, and R4 in relation to the impedance, Rp, of the tube 2 when it is conductive. Optimum results are obtained when the circuit relations are as follows: f

A repeating square-wave applied to the grid IS in tube 2 then causes tubes 3 and 4 to alternately conduct and block the passage of signals applied to their grids. A conductive state in tube 3 is established by rendering tube 2 conductive. This fact will be evident when it is seen that the cathode potential in tube 3 is substantially reduced by the shunting of a certain amount of current through the tube 2, thus increasing the potential drop through resistor R4.v The current in resistors R2 and RI is correspondingly reduced and the voltage on cathode I2 approaches ground potential. Under this condition, .the signals from channel A are amplified in the upper` section of tube 3 and are passed out on channel C. At the same time signals derived from the input channel B are amplified in the lower half of tube 3 and are passed out on channel D. n

"During the conductive state of tube 3, tube 4 is blocked by a considerable voltage drop in resistor R3, the, cathode resistor for tube 2. Tube 2 when it ris conductive has a relatively positive cathode in respect to ground potential and, therefore, the cathode I4 in tube 4 stands at a sufiiciently positive potential with respect toits grids two anodes I8 and 20. 85 8 and II so that this tube cannot conduct.

Assuming now that the signal potential in the control circuit E is such as to apply a negative bias to the grid I3, then tube 2 becomes blocked.

Now the cathodes l5 and I4 are substantially reduced to ground potential so that tube 4 becomes conductive. The signals applied by input channel A to the grid I and by input channel B to grid il become effective in tube 4 for amplii'ying A this condition persists, that is, a conductive state in tube 4, tube 3 is blocked by virtue of the relatively positive potential applied to its cathode l2 with respect to ground. This will be observed from the i'act that with tube 2 blocked, the voltage drop through resistors R4, R2, and RI is such as to maintain the desired positive potential on the cathode l2. 'Ihe grid potentials in the tubes 3 and 4 do not fluctuate with respect to ground other than in response to the signal voltages derived from the action oi transformers 8 and 9.

It will be. apparent that the double-pole doublethrcw switching function may be carried out in the above manner as often as may be desired. and either at regular or irregular intervals, all dedependent input circuits A and B, a pair of independent output circuits C and D, controllable electronic amplier means for feeding signals from each of said input circuits simultaneously to a respective one of said output circuit, and bias control means eilective to render diierent porpending upon the nature of the train of signals applied to theA terminals E. In certain applications, the switching operation may need to be pertions of said ampliiier means interchangeably conductive and non-conductive, one portion of said amplifier `means being arranged, when it is conductive, to direct signals from input circuit A Vto output circuit C while also directingl signals from input circuit B to output circuit D, the other portion of said amplifier means being arranged, when it is conductive, to direct signals from input circuits A and B into outputcircuits D and C respectively.

4. An electronic switching arrangement of the double-pole double-throw type comprising two independent input circuits, two independent output circuits, two discharge' tubes of the twin triode type, parallel connections from one of said input circuits to certain control grids, one in each of said tubes, parallel connections froml the other of said input circuits to the remaining control grids in said tubes, each of said output circuits havinlir parallel connections to appropriate anodes in both tubes, a direct current operating potential source having impedance connections to the electrodes of said tubes, and means including a controlled discharge device the space path in which comformed very rapidly and under control of the half cycles of an alternatingl current, either of very high frequency or of medium high frequency. On the other hand, the switching may be accomplished by means of a manual key in the circuit E, or it may be accomplished by a perforated tape transmitter such as is used in Morse telegraphy. Other control means may also suggest themselves to those skilled in the art.

system possesses no time constant circuits such as might interfere with the on-and-oil holding time for thetubes 3 and 4. In other words. the switching function may be performed independently of any time constants inherent in the circuit itself. The switching is substantiallyy instantaneous and is inertialess.

The applications of our invention to communications systems, and other electrical systems as well. are too numerous to mention. The scope of the invention should. therefore, be considered as broadly covering a great variety of such applications. y

s 1. A plurality of electron discharge devices baving a total of four discharge paths and constituted as a double-pole double-throw reversing switch, said devices having cathode grid and anode electrodes. mea-ns including a discharge tube for socontrolling the bias potential applied between the cathodes and control grids of said devices that conductivity is obtained in two of said paths as selected while the two remaining paths' are blocked, and means including an inout potential source applied to said discharge tube for interchanging the control eilects of the iirst said means.

2. 'I'he combination accordingto claim 1 and two independent output chan els coupled to the input and output sides res ctively oi said discharge devices. f

pletes a. potentiometer shunt circuit across the terminals of said source for producing a reversible voltage difference between the cathode of one tube and that of the other, whereby signals 85 delivered by each input circuit are simultaneously and independently transferred to a selected one of said output circuits. l

5. The method of performing an electronic `reverse switching operation as between each oi `40 two independent input circuits and each of two It will be noted that our improved switching independent output circuits, alternative space discharge paths being provided whereby signals delivered by each input circuit are amplified in one or-the other of said output circuits, which method comprises causing a control voltage of substantially square-wave formation to be amplined in still another discharge path, utilizing the transconductance of the last mentioned discharge path to diiferentiate between cathode potentials in respect to the discharge paths rst mentioned,

.causing the more' positive of said cathode poin a Wheatstone bridge circuit, a resistor of predetermined value in each of the other arms of said bridge circuit, a direct current operating pctential sou'rce for said switching arrangement and for said tube, said source having its positive terminal connected through a fixed impedance to one corner oi said bridge circuit and having its negative terminal connected to the opposite corner thereof, said switching arrangement having connections from points of csthodal potential there- 3. In an electronic switching arrangement of .Y in to the remaining two corners of said bridge the double-pole-double-throw type, a pair of incircuitl and connections from the positive termina] of said source to points of anodal potential in said switching arrangement.

7. The combination according to claim 6 and including control grids in the discharge paths of said switching arrangement, two of said grids in alternatively conductive paths being parallelconnected in coupling relation to one of said input circuits and two remaining grids being similarly connected in coupling relation to the other of said input circuits.

8. An electronic double-pole double-throw switch in combination with an electronic control device therefor, said device comprising a discharge tube responsive to control potentials of square wave form, a direct current operating potential source for said switch and said control device, input circuits A and B and output circuits C and D, two discharge paths in said switch having control grids responsive to signals derived from circuit A and having anodes independently coupled to circuits C and D, two remaining discharge paths in said switch having control grids responsive to signals derived from circuit B and having anodes each in parallel with one of the aforesaid anodes respectively, and means including resistive elements connected between the terminals of said source and cooperating with said discharge tube for causing a re-v versal of conductive states as between one pair and another pair of discharge paths in said switch.

9. In a device of the class described, two input signal channels A and B, two output signal channels C and D, and a square wave switching control source E, electron discharge switching means having cathode, anode and grid electrodes, and having at least two envelopes, separately enveloped grids being interconnected in pairs and each pair thereof being coupled to a respective one of the channels A and B, separately enveloped anodes which are opposed to grids of different pairs being connected in parallel and coupled to a respective one of the channels C and D, a bridge circuit including resistive impedances in three arms and a discharge tube in the fourth arm, a source of direct current operating potential for said switching means and for said tube, a potentiometer circuit connected across the terminals of said source and including a resistor in series with said bridge, and means including connections from each branch of said bridge respectively to the separately enveloped cathodes in said switching means for producing selective emission therefrom in dependence upon the control of said discharge tube by potentials from the source E.

10. Switching apparatus -for reversing the channels of communication between two input circuits A and B and two output circuits C and D, said apparatus including a twin triode discharge tube two discharge paths in which are commonly controllable for simultaneously passing signals from circuit A to circuit C and from circuit B to circuit D, a second twin triode discharge tube' 

